Magnetic random access memory (MRAM) promises fast reading/writing, high density, non-volatility and low power consumption, thus it is suitable for the information-processing instrument, such as computers, or cell phones, etc.; and has attracted extensive attentions.
The existing MRAM includes transistors configured as switches, and magnetic tunnel junction (MTJ) structures configured to store data. The basic concept of the MRAM is to apply a magnetic field to store information in MTJ structures; and to read the stored information by measuring the current in the MTJ structures.
FIG. 1 illustrates an existing MTJ structure. The MTJ structure includes a substrate 100, a bottom electrode 101 formed on the substrate 100, a magnetic structure 102 formed on the bottom electrode 101 and a top electrode 103 formed on the magnetic structure 102. The magnetic structure 102 includes a fixed magnetic layer 110, a tunnel insulation layer 111 formed on the fixed magnetic layer 110 and a free magnetic layer 112 formed on the tunnel insulation layer 111. The magnetic structure 102 includes at least three layers. Further, the MTJ structure also includes a first dielectric layer 104 between the free magnetic layer 112 and the top electrode 103; and a second dielectric layer 105 between the fixed magnetic layer 110 and the bottom electrode 101.
The magnetization direction of the fixed magnetic layer 110 is fixed; and the magnetization direction of the free magnetic layer 112 is programmable. When the magnetization direction of the free magnetic layer 112 is same as the magnetization direction of the fixed magnetic layer 110, the resistance of the MTJ structure is minimum, thus the MTJ structure is at the logic “0” state. When the magnetization direction of the free magnetic layer 112 has a 180° phase difference with the magnetization direction of the fixed magnetic layer 110, the resistance of the MTJ structure is maximum, thus the MTJ structure is at the logic “1” state. During a data reading process, the state of the MRAM is read by obtaining the resistance of the MTJ structure.
However, the storing performance of such MTJ structure may be unstable, and the reliability of the MRAM may be relatively low. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.